Alternating-current electric motor.



H. S. MEYER.V

ALTERNATING CURRENT ELECTRIC MOTOR.

APPLIOATION FILED AUG. 22, 190s.

980,986. Patented Jan. 10, 1911.

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UNITED STATES PATENT OFFICE.

m8 Gm 0F IBBEIEN, GERMANY, ASSIGNOB T0 GENERAL ELECTRIC COIPAN'Y, A CORPORATION 0F NEW YORK.

ALTEBNATING-CUBBENT ELECTRIC MQTCB.

To all whom it may concem:

. Be it known that I, HANs SIGIsMUND Meran, of Knig'Albertstrasse, Bremen,

' manager, a subject of the Emperor of Gerrent Electric Motors, of which the f many, residing at Bremen, Germany, have invented certain new and useful Improve ments in or Relating to Alternating-Curol owing is a specification.

This invention relates to alternating current electric motors of the kinduction type and more .especially to motors of that type in ywhich a starting winding of iron or other magnetic material is arranged in inductive relation to the stator or primary windin f yThe object of the invention is to simplify and cheapen the construction of the motor as well as to improve its etliciency by arranging the starting winding in groovesor slots in the secondary core member in the form of bars of magnetic material short-circuited on themselves by suitable means. In addition to the short` circuited winding, the rotor is provided with a copper, running winding of ordinary constructlon. The rotor grooves or slots Vmay communicate at their bottom end with channels,l in which the bars of the squirrel-cage winding are tightly fitted so as to form a single slot with two enlarged portions connected by a narrow portion. The

ends of the bars may pass through holes in the flanges of the armature spider and may be riveted to the same, the said flanges serving as end rings, and at the same time suplort and"`hold together the rotor laminations.

he short-circuiting flanges or rings may also be used for supporting the copper windotors, having 'iron squirrel-cage windings only, are well-known. On the other hand, armatures with auxiliary short-circuited windings of high resistance arranged in sections for starting, have also been previously constructed but such auxiliary windings have always been made of copper. The

useful cross-section of the iron is, however, decreased by the use of copper bars, and thus the output of the motor is also reduced, for the output approximately corresponds to the number of the lines of force which pass through the rotor, and, therefore, depends on the cross-section of the iron. Unlike well known constructions the use of iron bars according to the Y resent invention enables the cross-section o the armature to be mainpecilcation ot Letten Patent. Appunti ma august 22, isos. semi no. :$1,567.

Patented Jan. 10, 1911.

tained, and moreover, the resistance of the starting auxiliary winding is automatically reduced as the speed increases, owing to a property of magnetic'materials, as vhereinafter explained. The prence of the winding is also useful electrically when the motor is operating at full speed'.

For a better understanding'l of my invention reference may be had to the following description taken in connection with the accompanying drawing, in which- Figure 1 is a sectional view of the slots of an induction motor provided with my invention; Fig. 2 is aY section of the rotor on the line A--B of Fig. 1; Fi 3 is av diagrammatical representation o the rotor winding; Fig. 4 a'diagrammatical view of a switch for short-eircuiting the windin shown in Fig. 3, and Fig. 5 1s the sectiona view of the slots of an induction motor showin a modification.

Simiir reference numerals will be used `throu hout the specification and the several gures of the drawing to denote like parts The magnetic bars a are arranged in the lower portion and the copper winding c in the upper portion of the slots of the rotor d. Current is induced in these windings by the winding of the stator f. The bars may be made of iron and fit tightly in their portion of the slots. The bar Winding could also be arranged `in se arate grooves, as shown in Fig. 5. But t is latter arrangement would be considerably less advantageous from the lelectrical point of View, as

vso

the self induction of the bar winding would be increased. The laminae h are mounted onthe armature spider m and are held in place by the flanges g and g1, into which are also riveted the bars a.. One ofthe flanges y may be made integral with the armature spider, while the other g1' is held in place by bolts or rivets p. The lateral supporting arms i for the copper winding c are also secured to the llanges g and. g1. The flanges lcan be made either of magnetic or of nonmately equ-al tothe normal load current.

The squirrel-cage winding is designed so as to have low current densities therein, and as no insulating material or soldered joints are used, frequent starting, as wellas a temporary use of the squirrel-ca e winding alone, cannot do any harm. his simple winding forms the starting resistance, and as the bars a are made of magnetic material land fit exactly into the slots or channels,

the existence of these channels does not mean any increase of magnetic resistance. Thus the starting resistance in the rotor body is placed so as to effect the greatest saving of material, without affectlng the ventilation or the appearance of tne motor. A valuable property, referred to above, of this rotor consists 1n the automatic alteration of the resistance of the auxiliary winding, `owing to the so-called skin-effect. It is well known't-hat iron bars offer a considerably greater resistance to alternating currents of a large number of periods than tothose of a small number, and, therefore, the, resistance of the squirrel-cage winding is the greatest at starting and gradually decreases with the increase of speed of the rotor,.that is to say, with the decrease of the periodicity of the rotor currents. For a great portion of the starting period there is, therefore, no necessity for having any switchin In orer to increase the efliciency under normal running conditions, in addition to having an iron squirrel-cage winding, a copper, running winding c is employed. The copper winding is gradually cut into circuit after the motor has reached about of its normal speed, and in this case as it is only a question of increasing the speed by about 30%, 2 or 'sections will be sufficient in order to prevent heavy rushes of current. Were it not for the automatic variation of the resistance of the iron squirrel-cage winding and the consequently higher speed attained, av greater number of sections of the copper winding would have been required. This renders a very compact and simple construction of the starting switch for the copper winding possible. Since there is very litle liability to sparking at the points of contact, the switch can easily be inclosed, so that the motor can be used without any further alterations, even in places exposed to risk of fire. The contact points can be constructed in such a manner that the current passes first from metal to carbon, and then only to metal which, on the one-hand, contributes to further graduation of the starting current, and also renders any sparking that mighttake place inside the switch box harmless. A

During the normal operation of the motor, that is to say, after the whole of the copper winding has been short-circuited, the rotor currents become divided, in the proportion of the apparent resistances, between the irm and the copper windings, and in that way the efiiciency of the motor is increased during the wholeoperating period, as the squirrel-cage winding is in parallel with the copper winding and thus 'contributes to the decrease of slip. In itself` the copper winding could also be a squirrel-cage winding, but, as is well known, that increases the weight of the mechanical device for switching-in sections. For that reason a so-called phase winding has been selected, which, as shown in Fig. 3, is a two-phase-winding having two sections per phase with a grounded neutral point. The first section of the copper winding c, of Fig. 3, which is to be short-circuited, is brought to the terminals In, and the whole winding is included between the terminals l. The long terminals cl of the switch shown in Fig. 4 are short-circuited by means Yof the metal strap a, shown in dotted lines, and the short terminals ll are short-circuitedby the metal strip t, shown in full lines. The tips of the terminals k1 Aand l1 maybe made of carbon, as indicated in the drawing. By inserting the switch a short distance into the terminals of the winding so. that only they carbon tips make contact, the first section of the wlnding is short-circuited thro h the terminal k, the switch terminal 1, the metal bar s, the other switch terminal k1, and finally through the other winding terminal k. The winding terminals are hollow and permit the switch terminals to ass' through them, so that by pushing the switch Ain farther the short-circuit is made better by the co per parts of the switch terminals. A still rther movement of the switch brings the winding terminals l into contact with the carbon tips of the switch terminals Z1, and the whole winding is short-circuited by the metal strip t, in addition tothe shortcircuit of the first section of the winding. The final position of the switch brings the winding terminals l into contact with the copper part of the switch-'terminals l, and the short-circuit is complete. The squlrrelcage winding, consisting of iron bars, serves, therefore, not only as an indestructible starting resistance, but also is of great use mechanically, electrically and etically during the whole period of operatlon of the motor.

What I claim as new and desire to secure by Letters Patent of the United States, is,- 1. In an induction motor, a rotor ha laminations, said laminations having slots therein, a cop said slots in t e periphery of the rotor, means for short-circuiting said co per wind'- ing when said motor atta-ms and bars of magnetic material extending through seid laminations and suitably connected together to-form ashort-circuited winding.

r -winding distributed in' esops In an induction motor, a rotor having laininations, said laminat-ions having 'slots therein. a running winding distributed in .said slots in the periphery of the rotor, and bars of magnetic material extending through said laminations, said bars being located in the laniinations below the slots and suitably connected together to form a short-Circuited .starting winding.

3. ln an induction motor, a rotor having laminations, said laminations having slots therein, a. winding distributed in said slots iu the periphery of the rotor, means for short-circuiting said winding when the' niotor attains s eed, and bars of magnetic ma'. teria) exten ing through said laininations, said bars heilig locatedvin the laminations below the slots and suitably.connected together to form a short-circuited starting winding.

4. In an induction motor, a rotor ha ving a spider, laininations mounted thereon, flanges c amping said laminations, said laiiiinations having slots, said slots having an enlarged top portion and an enlarged bottom portion, a winding in said top irtion, bars of magnetic material fitting tightly in said bottom portion and being secured in said flanges so as to form a squirrel-cage winding.

In an induction motor, a rotor built up of laniinations, said laniinations having` slots.` bars of magnetic material in the bottom of 'said slots forming a squirrel-cage winding, a coppei` winding in the top of said slots and means for short-circuiting said copper winding when the. motor attains' speed, said bars-,of magnetic material being substantially Surrounded by iron.

Signed by ine at Bremen, Germany, this twentieth day of July 1906.

HANS SGISMUD MEYER. Witnesses:

C. DIEDERICH, J. REICH. 

